Pulse generating circuit



Feb. 13, 1947. D. E. MAXWELL 2,416,111

PULSE GENERATING CIRCUIT Filed June 19, 1944 SOURCE PULSE VOLTAGE Fig.3.

Inventor:- Donald E. Maxwell,

H is Attorney.

Patented Feb. 18, 194'? p 2,416,1ii

PULSE GENERATING CIRCUIT Donald E. Maxwell, Syracuse, N. Y., assignor toGeneral Electric Company, a corporation of New York Application June 19,1944, Serial No. 541,043

9 Claims.

My invention relates to electric pulse generating circuits, and moreparticularly to means for shaping the trailing edge of a pulse toprovide a more nearly rectangular pulse wave form.

' Many radio communication and detection circuits in current. use employpulse modulated rather-than continuous carrier waves for transmission.The modulating pulses are of very short duration, for example of theorder of 1 microsecond, and preferably are of substantially rectangularwave shape. The pulsed carrier wave may be utilized in various ways,such as by transmission and reflection of a series of pulses for objectdetection, or by signal modulation of the pulse width, amplitude, orfrequency to convey intelligence.

The pulse modulated carrier waves are commonly produced by generatingvoltage pulses of the desired characteristics and utilizing the pulsesto modulate the output of a high frequency oscillator, such as amagnetron oscillator or the like. In such modulating circuits a pulsetransformer is frequently interposed between the pulse generator and themagnetron oscillator, both to increase the voltage applied to themagnetron tube and to provide a charging path for the capacitivepulse-forming element.

In certain applications it is found desirable that a single apparatus becapable of supplying pulses of selectable duration or width, a typicalvariation in width being over a range of the order .of 5:1. Forexample,'a single pulse generator may be required to supply either a 0.5

mircosecond pulse or a 2.5 microsecond pulse. Heretofore, considerabledifliculty has been encountered in providing such a versatile pulsegenerating apparatus, especially where the pulse load circuit isinductive, as it is when a pulse transformer is used. Such transformermay be designed to produce desirably shaped pulses of only one width. Ifthe transformer is designed to produce a well-shaped wide pulse, anappreciably narrower pulse will exhibit a very slow decay of voltage atthe trailing edge; while, if the transformer is designed to produce awellshaped narrow pulse, the magnetizing current will be excessive onthe wide pulse, resulting in,

poor pulse efficiency and voltage reversal at the trailing edge of eachpulse. In either case, the trailing edge of each-pulse is characterizedalso by severe oscillations of very high frequency resulting from theleakage reactance and distributed capacitance within the pulsetransformer itself. On the other hand, a pulse transformer designed forpulses of intermediate width leaves much to be desired, because bothwide and" narrow pulses will then have unsatisfactory wave shapes.

Accordingly, it is one object of my: invention to provide a new andimproved pulse generating .voltage decay atthe trailing edge of eachpulse and means for suppressing trailing edge oscillations.

In accordance with my invention, I provide a pulse transformer designedparticularly. to pro vide an optimum wave shape for the widestcontemplated pulse. Such design demands; among other things, atransformer having a primary inductance sufficiently great that themagnetizing current and trailing edge oscillations will not beobjectionably large for the wide pulse. Such a transformer, however,does not store suflicient energy during the shortest contemplated pulseinterval to effect rapid decay of pulse voltage at the trailing edge ofthe pulse. Therefore, in order to provide sufiicient energy storage toavoid slow voltage decay at the trailing edge of a short pulse, Iconnect across the pulse transformer an inductive network arranged toincrease the effective magnetizing current and ener yv storage for shortpulses to a value suflicient to cause rapid decay of the pulse voltageat the trailing edge of a short pulse. Switching means are provided fordisabling the auxiliary inductive circuit when wide pulses are desired.Preferably, energy dissipating means is also provided across the pulsetransformer for preventing violent voltage oscillations at the trailingedge of the pulse, while permitting rapid voltage decay.

Myinvention will be more fully understood and its objects and advantagesfurther appreciated by referring now to the following detailedspecification taken'in conjunction with the accompanying drawingin'which Fig. 1 is a schematic circuit diagram of a pulse generatingcircuit embodying my invention and Figs. 2 and 3 are graphicalvrepresentations of pulse wave shapes illustrating the operation andeffect of my invention.

- Referringnow to the drawing, and particularly to Fig. 1, I haveshown-a pulse generating circuit comprising a source I of substantiallyrectangular voltage pulses of selectable width or duration. Thesuccession of pulses originating in the source I is supplied through atransformer 2 to the input circuit of an electron discharge device 3.The electron discharge device 3 comprises an anode 4,;a cathode 5, andacontrol vice or pulse triggering a tube 3 is periodically I renderedconductive by positive voltage pulses from the source I, thereby toconnect the condenser I for pulse discharge through an output circuitincluding an autotransformer 9 anda magnetron oscillator tube 8 havingan anode 8a and a cathode 8b.

As shown in the drawing, the magnetron oscillator tube 8 is connectedacross the secondary 'winding of the autotransformer 9, the primarywinding! of which is connected in parallel circuit relation with thepulse discharge path through the magnetron oscillator 8. The primarywinding II! of the autotransformer 9 serves as a direct current path forrecharging the condenser 1- at the termination of each pulse. Thecondenser charging circuit also includes a high resistance II and asource of unidirectional electric current supply, such as the battery[2, connected in series circuit relation between the anode and cathodeof the electron discharge device 3. The cathode 5 of the dischargedevice 3 and the anode 8a of the magnetron oscillator 8, as well as thenegative terminal of the battery l2 and one terminal of theautotransformer 9, are connected together and grounded, as shown at Fig.1.

The input circuit for the pulse triggering tube 3 comprises a secondarywinding l3'of the input transformer 2 connected between the oathode 5and control electrode 6 of the discharge device 9 through a suitablecoupling capacitor M. The discharge device 3 is negatively biased tocut-off by any suitable means, such as, for example, a battery liand agrid resistor l6 connected'betweenithe cathode 5 and control electrode6.

It is found in practice that the autotransformer 9 and the magnetronoscillator tube 8 have a certain amount of stray and distributedcapacitance to ground. This capacitance is m dicated at it by dottedlines in Fig. l as capacitance between the anode and cathode of themagnetron 8. The stray and distributed capaci-i ties represented by thecapacitor 8 form with the autotransformer 9 a resonant circuit having anatural frequency of oscillation relatively high with respect totherepetition rate of the pulses from the source, i. This naturaloscillation frequency is ordinarily of the order of 100 kilocycles persecond. The pulse repetition rate, on the other hand, is ordinarily ofthe order of 500 to 5000 pulses per second in radio detection apparatusor pulse communication apparatus. The autotransformer 9 has also acertain amount of internal leakage inductance and distributed ca:v

'pacitance.

In pulse transformers of the type commonly employed in the generation ofpulses of the character described, these internal circuit constants tendto initiate a very high frequency.

trailing edge oscillation superposed upon the 100 kilocycle oscillationdescribed above. These superposed high frequency oscillations areordinarily of the order of 7 to 10 megacycles per second.

' The autotransformer 9 is designed to provide microseconds." Since theautotransformer is connected in parallel circuit relation with the- 4tor tube 8, such design demands that the transformer be provided withsufiicient inductance so that the energy stored in the transformerduring the relatively long pulse will not be so great as I to produceundesirably violent high frequency oscillations in the resonant circuit9, It at the termination of 7 av pulse. On the other hand, thetransformer inductance must permit sufficient magnetizing current andenergy storage to effect a rapid decay of pulse voltage at the pulsetermination. A transformer designed to meet these requirements in theoptimum manner will have such a high inductance that appreciably shorterpulses, for example of the order of 0.5 microsecend, will not storesufiicient energy in the transformer to efiect a rapid decay of pulsevoltage at.

the termination of the pulse. Accordingly; for

such short pulses, the trailing edge of the pulse will demonstrate agradual decay of voltage,

an optimum pulse. wave shape for the pulses of; longestdurationcontemplated, for example 2.5

rather than a sharp decay as desired.

In order to improve the characteristics of my pulse generating circuitfor short pulses, I provide in parallel circuit relation with theprimary winding I 9 of the autotransformer 9. an inductive circuitincluding an inductive impedance [9 connected in series circuit relationwith a resistor 29 througha contact 2| of an electromagnetic relay 22.The relay 22 is controlled in any desired manner to connect the network19, 29 in parallel circuit relation with the transformer primary windinglil when short pulses are being generated and to disable the network I9, 29 when long pulses are generated. When the network [9, 20 isconnected in circuit with the transformer, the effect of the network isto store additional energy in the inductive impedance l9 during thepulse intervals thereby to increase the effective magnetizing currentand to increase the stored energy available for release at thetermination of each pulse. The sum of the energy now stored in thetransformer 9 and the inductor I9 is suflicient to produce a rapid decayof pulse voltage at the trailing edge of each pulse. The additionalstored energy of course adds to the tendency to produce oscillations inthe kilocycle range at termination of each pulse. In order to maintain.such oscillations within practical'limits, the resistor 29 is providedand is of such value that the trailing edge oscillations in, the 100kilocycle range are rapidly damped out. 7 7

From the foregoing explanation, it is to be noted that it is necessaryto design the autotransformer 9 itself so that, for long duration pulseswith the network [9, 20 disabled, the energy storedin the transformer 9itself is sufiicient to produce a rapid decay of pulse voltage at thetrailing edge While the network I9, 29 is so designed kilocycles,additional means is necessary for suppressing the highfrequency'oscillations at about Z to 10 megacycles arising from theinternal circuit constantsof the pulse transformer 9. itself." 'F'orthis purpose, an additional damping, resistor 23 may be'connected inseriescircuit relation with ablocking capacitor 24- across the primarytron discharge device 3 is normallybiased tocut" off by the battery Hi.When the discharge device 3 is not conducting, the condenser! ismaintained charged to substantially the full voltage of the battery 12througha charging circuit comprising the resistor H, the condenser 1,and the primary winding .ll! of the autotransformer 9. The voltagepulses applied from .the source I through'the transformer 2 are arrangedperiodically to impress positive potentialsupon the control electrode 6for predetermined pulseperiods therebytorender the, discharge device 3conduc-. tive. When the discharge device 3 becomes conductive, thecondenser 1 .idischarges through a load circuit comprising the dischargedevice '13,

the magnetron oscillator tube '8, and the upper portion of theautotransformer 9 The voltage drop through the discharge device 3 isrelatively small so that substantially the full .voltage of thecondenser 1 is impressed across the magnetron oscillator tube '8 andthe'upper portion of the autotransformerll. i

It will be noted, that there isconnected also across this load circuitthe primary windingv H! of the autotransformerm However, since theautotransformer primary winding Innis highly inductive, very littlemagnetizing current flows through the primary winding during the pulseperiod. During the period of the pulse, however, a small amount ofmagnetizingcurrent is gradually'louilt up in the transformer winding! l3so,

that at the termination of the pulse acertain amount of energy is storedin the windin I0.

This stored energy produces 'a rapid decay of voltage at the terminationof the pulse discharge and initiates both' a relatively lowfrequencyLos-'- cillatory charge and discharge of the distributed andstray capacitance represented by thecondenser I8 and the high frequencyoscillations characteristic of the internal transformer circuitconstants. When the inductive reactor I9 is notconnected in thecircuit,the lower frequency oscillations .are'not of objectionableamplitude,-and the high frequency oscillations are damped by the network23,24. When short pulses are received from the trigger voltage source I,the inductive network [9, 20 is connectedin circuitin order to storesuflicient energy to efiect rapid trailing edge pulse voltage decay. Thereactor l9 increases the tendency of the circuit to developoscillationsin the range of 100 kilocycles, but-the-resistor 20 'effectssatisfactory damping of suchoscillations; The network 23,24 functions asbefore to damp the high frequency oscillations at 7 to 10 megacycles,but is relatively ineffective for the lower frequency oscillations.

'To illustrate the effect of the networks I9, 29 and 23, 24 connected inparallelgcircuit relation 4 of shorter duration than said 'maximum, and

. v e I winding of the pulse transformer '9 when the transformer 9 isdesigned t'o-provide 2.5 microsecond pulses and the networks I9, 20 and23', 24 are not connected in circuit with the transformer. At diagram bof Fig. 2, Ihave illustrated a typical wave shape for a 0.5 microsecondpulse'as obtained from the same transformer under similar conditions.Referring now to Fig.3, I have shown similar diagrams a; and billustrating the waveshapes of 2.5 and 0.5 microsecond pulses,respectively, which are obtained from the same transformer 9 when thenetworks I9, 29 and 23, 24 are connected in parallel circuit relationprimary winding [0. Y

While I have described only one preferred bodiment of my invention byway of illustration, many modificationswill' occur to those skilled inthe art and'I therefore wish to have it understood that I intend in theappended claims to cover all such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is z" 1. In combination, acapacitive pulse-forming energy storageelement,.-a'load circuit including an inductive energy storagejelement,means for establishing a succession of pulse discharges of saidcapacitive storag'eelement through said load circuit, said meanscomprising switchingmeans.

and means for rendering said switchingmeans conductive for recurrentpulse interval of selectable duration, saidinductive element-storingsufiicient energy during pulse intervals of maximum duration to effect arapid voltage decayat the termination of eachsuch pulse interval, and

an additional inductive energy storage element arranged to be connectedinparallel circuit relation with said first inductive element tofacilitate the'formation of pulses of shorter duration than saidmaximum.

2. In combinatiorua capacitive pulseiforining storage element, a loadcircuit including an in- .ductive energy torage element; mean's forestablishing a succession of pulse dischargesof said capacitive storageelement through said load circuit, said means comprising switching meansand means for rendering said-switching means conductive for recurrentpulse intervals of selectable duration, said inductive elementstoringsuifi c'ient energy during pulse intervals of maximum dura tionto effect a rapid decay of voltage at the termination of eachpulseint'erval', mean in cluding a-sourceof electric current supplyq'forcharging said capacitivestorage element between said pulse intervals,an. additional inductive energy storage element arranged to beconnected, in parallel circuit relation with said firstinductiveelementto facilitate the formation of pulses means for damping electricoscillations'initiated by said stored energy at the termination. of eachsaid Pulse discharges comprising a resistor connected in series circuitrelation withsaidadwith the primary winding ID of the autotransformer 9,I have shown at'Fig. 2 a diagram a illustrating a typical pulse waveshape fora 2.5 microsecond pulse obtainedfrom the secondary ditionalinductive energy storage element. 1

3. An electric pulsegenerating circuit comprising a capacitivepulse-dormingstorage element,

a load circuit including anjinductive energy storage element, means forestablishing a succession of pulse discharges of said capacitive storageele-' ment through said load circuit, said means com 1 prising switchingmeans and means for rendering said switching means conductive forrecurrent pulse intervals of selectable duration, said induc-"y I tiveelement storing sufficient energy during pulse intervals ofmaximumduration to. effectarapid' with the decayof voltagezatlthetermination of each pulse interval, :means iincluding a source .ofelectric current supply. for charging said capacitive storage elementbetween said ,pulse intervals, and

means for facilitating the. formation oipu'lses of shorter durationthansaid maximum comprising an additional inductive energystorageelement and a'rresistor arranged selectably to beconnected incircuit with .said ,first inductive energy storage element. t

4. An electric pulse generating circuit-compris ing a: capacitive lpulse-forming energy: storage element, a ioadcircuit includingaunidirectional. conducting device, means for .es'tablishingia'successionoflpulse discharges offsaid capacitiverstor age element throughsaid load :circuit. including switching meanandmeans'forrecurrentlyrendering saidjswitching means conduc'ti've.iorpulse intervals of selectable duration, means including an inductiveenergy storage element connected across said unidirectionalconductingdevice, said inductive element storing sufficient.energyduring pulse intervals of maximum duration to efiect a rapidvoltagedecay at the termination of each pulse interval, and an:additional inductive en-i ergy storage element arranged selectably .:tobe energy istorage :elementga :loadiciircizit iincluding an inductive'zenergyrrstorage element, ,means for establishing :a succession ofpulse discharges of said capacitive storage element through saidjloadcircuit, said :means comprising (switching means and means for rendering"said switching means conductive i011.reourrent'apulse intervals lot:so;-

lecta'bl'e Iduratio 11,, said inductive element storing sufiicientenergy. during :pulse :intervals of maxi-i mumiselectable duration :toaeffecta rapid voltage dec'aylat ithe'itermination :of reach :such pulseinterval, .a second :inductive energy storage .Iele

- ment, switching means formonnecting'said secconnectedinseriescircuitrelation with a resistor across said "first inductive energy. storageelement during theformationlof pulses oflshcrter duration than saidmaximum. r v

7 -75. In combination, an, electron dischargedevice including an anode,a cathodaand ascontrolJelec trode,'means for supplying to said controlelectrode a succession of voltagefpulses of selectabledurations-arranged recurrently to render said dis- I charge deviceconductive forpredetermined se-v lectable pulse intervals, a capacitivepulse-formj ingenergy storage element, a load circuit icon? 0ndinductive energylstorage element in parallel circuit "relation with saidfirst inductive energy storage element thereby to. increase theefi'ective I magnetizing'current ofcsaidyload circuit for pulses ofshorter duration than said maximum, and means for damping electricoscillations initiated 1 by said stored energy-at the termination ofeach pulse discharge comprising a resistor connected in parallelJcircuit relation with said first energy storage element. v l s j '8.IIn combination, an :electron discharge :de-

"vice including antanode; a cathode, and a control electrode, :meansforsupplying tosaid icont'rol electrode a succession of voltagepulses ofselectable duration arranged recurrently to render .said dischargedevice conductive for predetermined selectable pulse intervals, a capaci.tiveipulsefor'ming energy storage element, a load, 7 Q circuitincludingan autotransformer 1 having av primarywinding connectedacrosssaid capacitive pulse-forming element through said dischargedevice,said.v load cirouit gincluding also a unilateral conducting deviceconnected across ithe second},

' ary win-ding'aof said transiormerjthe :magnetizing' :current 20fsaidtransformer :being 'sufiicient nected to said capacitive storage elementthrough said discharge device, said load circuit-including.v aninductive energy storage element having a magnetizing current sufiicientto provide a rapid voltage decay at the termination of pulses of,

maximum selectable duration, a second inductive energy storagegelement,and switching meangfor connecting said inductive storage elements inparallel circuit relation to increase the'eiiective vice including-ananoda-a cathodeQanida control electrode, means for supplying to saidcontrol electrode a succession of,voltage pulses off-so"- lectableduration arranged recurrently to renderv said discharge deviceconductive forpredeter- I magnetizing current in said load circuitthereby to facilitate the formation oiv pulses oi shorter duration thansaid maximum. 1 -s so 6. In combination, an electron dischargedemined'selectable pulse intervals, a capacitive pulse-formingenergystorage element, aload circuit connected ,to'jsaid capacitivestorage element I 1 through said discharge device, 'saidload circuit 1including an autotran-sformer and a unidirection-l ally conductingdeviceconnected across; the. 1 transformer-secondary winding, the magnetizingcurrent of said transformer storing sufiicient en- Y j ergy in saidtransformer during pulses of maximum selectable duration to providearapid volt- 1' age decay at the termination of eachsuch pulse, 1 andmeans for increasing the effective magnetizing current ofsaidtransformer for pulses of i shorter duration than said maximumcomprising; 7 1 an inductiveenergystorage element and' an en- 1 ergydissipating resistor arranged foriselecta'ble connection'in parallelcircuit'relation' with the primary'windingiof said transformer.

T 3 In combination; a capacitive pulse-forming for pulses of maximumduration to effect rapid voltagev decaylof said pulses at thetermination thereof, 'meansfor increasing the effective image,

netizing current of :saidtransformer vcomprising an inductive :energystorage element, switching means forzconnecting said inductive energystorage element in parallel circuit relationwith the primary winding ofsaid 'autotransfiormerduring the occurrence of pulses of shorter saidmaximum; andilmea ns. for suppressing high frequency electricoscillations across said trans;

former atth'e termination of eachrpuls'e discharge yfor connecting saidload circuit to, said pulse-J forming element for pulseiintervals ofselectableduration, said inductive element storing sufficientenergyduring pulses of maximum' duration to er feet Ia rapid voltagedecay. atlthe termination'of I each such pulse, and means for selectablyincreasing the inductive energy storage capacity of said load circuitthereby to facilitate the formation of pulses of shorter duration'thansaid maximum.

DONALD 13.1 MAXW LL,

REFERENCES CITED The following references are of record inthe filelofthisipatentL V i 'FoREI-GNEPATENTSr Country Number :Date

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